Flash memory is known as small-size memory device and used to store data or program in storage device. The flash memory is roughly categorized into NOR-type and NAND-type.
The NOR-type flash memory can be accessed by random accessing method. Also, the NOR-type flash memory is expensive in price per storage capacity and is lower density than the NAND-type flash memory.
The NAND-type flash memory is not expensive and is higher density than the NOR-type flash memory. However, NAND type flash memory should be accessed by page as access unit. For example bytes contained in a page are 512 bytes. Moreover, each of data in a page must read or write in sequentially.
For this reason, a CPU (Central Processing Unit) and the like cannot read or write in directory the program or the data that stored in NAND-type flash memory using random accessing method to execute its instruction or to read/write the data.
The conventional storage device comprises NAND type flash memory is using simulated accessing method by program or device driver to enable random accessing from the CPU. The program or device driver is stored in nonvolatile memory that can access random addressing from the CPU. The nonvolatile memory is a NOR type flash memory or programmable ROM (Read Only Memory) and the like.
After power-on or reset, the CPU reads the program or device driver from the nonvolatile memory and stores the program or device driver to RAM (Random Access Memory). Then the CPU executes the program or device driver for reading and writing the data to/from NAND type flash memory using random accessing method.
However, according to the aforementioned technique, expensive NOR type flash memory is required to store the device driver. For this reason, the structure of storage device becomes complicated to increase in the size, resulting in an expensive storage.
The fundamental structure and operations of the NAND-type flash memory are explained in the catalogue of TC58128AFT (TOSHIBA), for example.